Infrared sensors detect infrared emission from objects at wavelength between about 8 μm to 14 μm that are not visible to human eyes, CCD or CMOS cameras. Traditional infrared sensors are fabricated using narrow band gap semiconductors or microbolometers, and they are difficult to make and expensive. Currently, there are some technologies that convert infrared signals into visible signals, and obtain the infrared image by calculating the infrared signal from the detected visible signals. One technology uses Micro-Electro-Mechanical Systems (MEMS) technology to manufacture infrared sensor array, i.e., focal plane array (FPA). In these structures, the supporting beams are made of different materials having different coefficients of thermal expansion (CTE), and when the absorbing plate absorbs incident infrared light, and transmits the absorbed heat to the supporting beams, the temperature of the supporting beams rises, and the supporting beams and the absorbing plate (also acts as a reflecting plate) bend, causing the reflected visible light to deflect. The intensity of the incident infrared light can be calculated by detecting the deflection angle of the visible light. This method measures the deflection of the visible lights, and involves complicated readout optical setup. Its manufacturing process is also difficult to control.
There are other technologies that convert infrared signals into visible signals, such as described by CN1427251A. The technology uses optical crystal which is difficult for production. The optical setup is also complicated, and the detected infrared light is from active infrared illumination, not infrared light emitted from objects.
Therefore, a simple, efficient, sensitive and accurate infrared sensor is needed for detecting infrared lights emitted by objects.
This invention provides a novel infrared sensor, focal plane array, and infrared imaging system for detecting infrared emissions from objects. This invention overcomes the disadvantages of existing technologies, and can accurately and speedily detect infrared emissions from objects, and convert the infrared emissions to images.
In accordance with one aspect of this invention, it is provided an infrared sensor that detects infrared emission from objects, wherein said infrared sensor comprises a first film structure, a second film structure, and a gap between said first film structure and said second film structure. When a reference light is incident on one of said first film structure and said second film structures, it is partially reflected and partially transmitted through the other film structure. When said gap between said two film structures changes, the intensity of the reflected reference light changes, as well as the intensity of the transmitted reference light. When an infrared light is incident, at least one of said first film structure and said second film structure absorbs incident infrared light, changes its temperature, and causes the gap to change consequently. By detecting the changes in the intensity of the reflected or transmitted reference light, the incident infrared light can be measured.
In accordance with another aspect of this invention, said infrared sensor further comprises a substrate, one or more first supporting mechanisms that support said first film structure on said substrate, wherein said second film structure is located directly on said substrate.
In accordance with another aspect of this invention, said infrared sensor comprises a substrate, one or more first supporting mechanisms that support said first film structure on said substrate; and one or more second supporting mechanisms that support said second film structures on said substrate.
In accordance with another aspect of this invention, said first supporting mechanism or said second supporting mechanism has the same layer structures as said first film structure or second film structure that it supports.
In accordance with another aspect of this invention, said second film structure and said substrate is an integrated structure.
In accordance with another aspect of this invention, part of said substrate is etched away to form an empty space. Said reference light is incident from the empty space and incident on said first film structure and said second film structure or incident on said first film structure and said second film structure and passes through said empty space. Infrared light is incident from the empty side or, from the opposite direction, incident to said first film structure or said second film structure.
In accordance with another aspect of this invention, to increase the absorption of the infrared light by the sensor, one of said first film structure and second film structure that is away from the incident infrared light is an infrared reflective film, or consists of an infrared reflective film on the upper surface, lower surface or somewhere in the middle. The infrared reflective film as described in this invention is film made of materials that have strong reflectivity for infrared emissions, including all conductive materials, such as metal and transparent conductive material such as ITO. In accordance with another aspect of this invention, transparent conductive materials such as ITO, InZnO and ZnO are used to make the infrared reflective film in the transmission mode.
In accordance with another aspect of this invention, in order to increase infrared absorption by the sensor, one of said first film structure and said second film structure that is on the incident infrared light side is an infrared absorbing film, or consists of an infrared absorbing film on the upper surface, lower surface, or somewhere in the middle. The infrared absorbing film as described in this invention is film made of materials that have strong absorption for infrared emissions at wavelength between 8 μm to 14 μm, including materials that have absorption peak for infrared lights at wavelength between 8 μm to 14 μm.
In accordance with another aspect of this invention, said first supporting mechanism of the sensor comprises a beam having one end attached to said first film structure and another end attached to said substrate, said second film structure, or said second supporting mechanism; an additional layer attached with said beam. Said second supporting mechanism comprises a beam having one end attached to said second film structure and another end attached to said substrate; an additional layer attached with said beam. Said beam consists of a material or material combination with a first CTE, said additional layers consist of a material or material combination with a second CTE. Said first CTE is different from said second CTE. Said first and second supporting mechanisms include straight beams, spin-wheel structures, and symmetric structures.
In accordance with another aspect of this invention, part of said beam has additional layer on the upper surface, and part of said beam has additional layer on the lower surface.
In accordance with another aspect of this invention, said first or said second mechanism is a microbridge that supports said first film structure or the second film structure. Said microbridge has at least two beams. Said beams may not have an additional layer.
In accordance with another aspect of this invention, in said infrared sensor, said first and second supporting mechanisms bend in the same direction when the environment temperature changes so as to keep the gap between said two film structures unchanged. Said environment temperature as described in this invention is the temperature of the environment in which the infrared sensor is located, not the temperature of the objects that the sensor detects.
In accordance with another aspect of this invention, said first film structure and said second film structure are reflective mirrors respectively, creating interference between said first film structure and said second film structure.
In accordance with another aspect of this invention, said first film structure and said second film structure consist of multiple layers of materials. Said multiple layers of materials include symmetric structure, wherein the types of materials are vertically symmetric while the thickness of layers may or may not be symmetric, such as 100 nm SiNx/100 nm SiO2/200 nm a-Si/120 nm SiO2/80 nm SiNx.
In accordance with another aspect of this invention, said first film structure, said second film structure consist of a single layer or multiple layers of materials. Said single layer or multiple layers of materials include silicon oxide (SiO2), silicon nitride (SiNx) or amorphous silicon (a-Si).
In accordance with another aspect of this invention, said first film structure and said second film structure consist of multiple layers of materials. Said multiple layers of materials include 5 layers of symmetric materials: a-Si/SiO2/a-Si/SiO2/a-Si, or SiNx/SiO2/a-Si/SiO2/SiNx.
In accordance with another aspect of this invention, said first film structure and said second film structure consist of a single layer or multiple layers of materials. The thickness of each layer in said single layer or multiple layers of materials is quarter wavelength of the reference light in the material.
In accordance with another aspect of this invention, said first supporting mechanism or second supporting mechanism includes: one or more beams consist of one or more materials with a first CTE; multiple additional layers attached to said beams, wherein said additional layers consist of one or more materials with a second CTE; wherein said additional layers are arranged such that: when the environment temperature changes, said first supporting mechanism or said second supporting mechanism bend in such a way that the displacements cancel each other and the gap keeps unchanged. When there is incident infrared light, the temperature of at least one of said first film structure and said second film structure rises, causing said first supporting mechanism or said second supporting mechanism to bend, the combination of all the bending results in a change in said gap distance.
In accordance with another aspect of this invention, said first or second supporting mechanism consists of three sections: a first section that is close to the substrate or has good thermal contact with the substrate, a second section that is close to said film structure that is supported by said supporting mechanism or has good thermal contact with said film structure, and a third section that is thermally insulating and located between the above two sections. In accordance with another aspect of this invention, in said first or second supporting mechanism, said first section that is close to the substrate or has good thermal contact with the substrate and second section that is close to said film structure that is supported by said supporting mechanism or has good thermal contact with said film structure bend in opposite directions when the temperature changes.
In accordance with another aspect of this invention, said first or second supporting mechanism contains first additional layer or layers and second additional layer or layers, wherein said first additional layer or layers and second additional layer or layers has two sections. Said total four sections are arranged as following: first section of first additional layer or layers, second section of first additional layer or layers, first section of second additional layer or layers, and second section of second additional layer or layers are sequentially attached to the beam, wherein first section of first additional layer or layers and second section of second additional layer or layers are attached to the same side of the beam; said second section of said first additional layer or layers and said first section of the second additional layer or layers are attached to the same other side of the beam.
In accordance with another aspect of this invention, at least one film structure in said first film structure and said second film structure absorbs light at wavelength outside of the infrared light spectrum, and the sensor is used to detect lights at such wavelength.
In accordance with another aspect of this invention, said substrate contains other devices or circuits, such as CMOS or CCD imaging devices or circuits.
In accordance with another aspect of this invention, when said infrared sensor operates at transmission mode, said infrared reflective film is transparent to said reference light. When said infrared sensor operates at reflectance mode, said infrared reflective film structure is transparent to said reference light or is metal.
In accordance with another aspect of this invention, a blind pixel is provided to sense the environment temperature of the sensor. Said blind pixel comprises a substrate, a first film structure, a second film structure, a gap between said first film structure and said second film structure. Reference light is incident on one of said first film structure and said second film structure, and transmits from the other film structure. When said gap changes, the intensity of said reflected reference light or said transmitted reference light changes. At least one of said first film structure and said second film structure absorbs infrared light and has good thermal contact with said substrate. When infrared light is incident on said first film structure and said second film structure, said gap between said first film structure and said second film structure does not change. When environment temperature changes, said gap distance changes. By detecting change in the intensity of said transmitted reference light from said second film structure, the environment temperature of the device is measured. Furthermore, the supporting mechanism of said blind pixel has high thermal conductivity, or has a large width, thickness or cross section area, or has multiple beams that increase the thermal conductivity between said first film structure or said second film structure and said substrate.
In accordance with another aspect of this invention, the film structure between said first film structure and said second film structure of said blind pixel that is at the same side of the incident infrared light is an infrared reflective film, or contains an infrared reflective film on the upper surface, lower surface, or somewhere in the middle.
Another blind pixel comprises: a substrate, a first film structure attached to the substrate, a medium attached to the first film structure, and a second film structure attached to the medium, wherein said first film structure, medium and second film structure forms an interferometer. When infrared light is incident on said first film structure and said second film structure, the refractive index of said medium does not change. When environment temperature changes, the refractive index of said medium changes, causing the intensities of the transmitted reference light and the reflected reference light from said first film structure and said second film structure to change. By detecting the change in the intensity of said transmitted reference light from said second film structure or said reflected reference light, the environment temperature of the device is measured.
In accordance with another aspect of this invention, said interferometer is connected to the substrate by a supporting mechanism, and has good thermal contact with the substrate.
In accordance with another aspect of this invention, said interferometer contains infrared reflective film on the upper surface, lower surface, or somewhere in the middle.
In accordance with another aspect of this invention, a focal plane array is provided that contains one or more of the infrared sensors of this invention. Furthermore, another focal plane array is provided that contains one or more of the blind pixels provided in this invention.
In accordance with another aspect of this invention, an infrared imaging system is provided that contains: a reference light source, a focal plane array in accordance with this invention, a detector for detecting the intensity of the reference light. The reference light source can be a LED; the detector can be a CCD or CMOS imaging chip.
This invention utilizes the principle of optical interference and has high sensitivity. Directly detecting the intensity of transmitted or reflected light, not deflection, is easy to implement. This invention uses the gap as a resonance cavity. The suspending reflecting layer is just a reflective film structure and has low thermal capacity. As a result, the sensor has fast response time. The gap changes sensitively when the temperature changes, and the sensor has high temperature resolution.